(a) Field of the Invention
The present invention relates to a method for manufacturing an electronic device such as a semiconductor device. In particular, it relates to a method for removing a deposit containing titanium fluoride, thereby improving yield of the manufacture of the electronic device.
(b) Description of Related Art
In recent years, for the purpose of improving properties of semiconductor devices in a semiconductor integrated circuit combined with DRAMs (Dynamic Random Access Memories), Ta2O5 and TiN have been used as a capacitor insulating film and a top electrode, respectively. Hereinafter, with reference to the drawings, an explanation is given of a conventional method for manufacturing a capacitor of a semiconductor device.
FIGS. 11A to 11D and FIGS. 12A to 12C are flow diagrams illustrating the conventional steps of manufacturing the capacitor.
First, as shown in FIG. 11A, a silicon oxide film is formed on a semiconductor substrate 10 made of silicon as a first interlayer insulating film 11. Then, a Ta2O5 film 12 is formed on the first interlayer insulating film 11 by CVD (Chemical Vapor Deposition) as a capacitor insulating film. Then, a TiN film 13 is formed on the Ta2O5 film 12 by CVD or PCD (Physical Vapor Deposition) as a top electrode.
Subsequently, as shown in FIG. 11B, a resist pattern 14 having an opening 14a is formed on the TiN film 13 by a common lithography technique.
Then, as shown in FIG. 11C, the TiN film 13 and the Ta2O5 film 12 are dry-etched by a common technique using the resist pattern 14 as a mask. For example, the etching is carried out by RIE (Reactive Ion Etching) using CF4 as etching gas at a flow rate of 20 ml/min (standard conditions) under pressure of 1.5 Pa and high frequency power of 600 W. Thereafter, the resist pattern 14 used as the mask is removed by ashing using O2 gas at 200° C., for example.
In this manner, an opening 20 penetrating the TiN film 13 and the Ta2O5 film 12 is formed to expose part of the first interlayer insulating film 11. At this time, an organic residue 15 remains in the opening 20. Further, as detailed later, a deposit 16 may be generated in the opening 20.
Then, as shown in FIG. 11D, the remainder (not shown) of the resist pattern 14 and the organic residue 15 in the opening 20 are removed by cleaning. For example, the cleaning is carried out using a polymeric cleaning solution containing amine at 70° C. for 5 minutes.
The polymeric cleaning solution containing amine is a polymeric cleaning solution which is used for cleaning semiconductor substrates including metal films and contains mainly amine, a chelating agent, a pH adjuster and the like. Although APM (ammonium hydrogen peroxide mixture: NH4OH/H2O2) is well known as a cleaning solution for the semiconductor substrates, APM is not included in the amine-containing polymeric cleaning solution mentioned herein. If SPM (sulfuric acid-hydrogen peroxide mixture: H2SO4/H2O2) is used as the cleaning solution, H2O2 contained therein oxidizes and dissolves the metal film. Therefore, SPM cannot be used in this step.
Even through this step, the deposit 16 is not removed and remains as it is.
Then, as shown in FIG. 12A, a silicon oxide film is formed on the TiN film 13 by CVD as a second interlayer insulating film 17. The second interlayer insulating film 17 fills the opening 20, thereby burying the deposit 16 below the second interlayer insulating film 17.
Then, as shown in FIG. 12B, the second interlayer insulating film 17 which filled the opening 20 is subjected to dry etching or the like to form a contact hole 17a reaching the semiconductor substrate 10.
The contact hole 17a is formed so as not to contact the TiN film 13 and the Ta2O5 film 12. However, if the deposit 16 exists, the deposit 16 may be exposed in the contact hole 17a. 
Then, as shown in FIG. 12C, tungsten is deposited by CVD to fill the contact hole 17a, thereby forming a contact plug 18. If the deposit 16 is exposed in the contact hole 17a, the contact plug 18 comes into contact with the deposit 16.
In this manner, the conventional capacitor is formed.
In the step shown in FIG. 11C, halogen-based gas is generally used to dry-etch films containing refractory metal such as the TiN film 13 and the Ta2O5 film 12. At this time, if fluorine-based gas is used and left as it is after the etching, the fluorine remainder reacts with metal, thereby generating metal fluoride as the deposit 16.
For example, Japanese Unexamined Patent Publication No. H6-151383 proposes a method for removing alkali metal fluorides or alkaline-earth metal fluorides remaining on the semiconductor substrate by oxidation using oxygen plasma or an oxidant solution. Therefore, if the deposit generated is alkali metal fluoride or alkaline-earth metal fluoride, the deposit 16 is removed from the resulting capacitor, unlike the one as shown in FIG. 12C.